System configurations and method for controlling image projection apparatuses

ABSTRACT

A projection apparatus implemented with a mirror device that includes a first electrode and a second electrode with an elastic hinge disposed between the first electrode part and second electrode. The elastic hinge supports a mirror and the mirror is controlled to deflect when drawn by a Coulomb force generated between the mirror and electrodes by applying a voltage to the electrodes. The projection apparatus further includes a light source for projecting a light to the mirror for modulating the light by deflecting the mirror to different deflection states. The light source suppresses the emission of the illumination light during a period when the mirror performs a series of operations to shift from a non-deflection state, placing the mirror in a stationary and non-deflection state, to a predetermined deflection state.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Non-provisional application claiming a Prioritydate of Oct. 2, 2007 based on a previously filed Provisional Application60/997,478 and a Non-provisional patent application Ser. No. 11/121,543filed on May 3, 2005 issued into U.S. Pat. No. 7,268,932. Theapplication Ser. No. 11/121,543 is a Continuation In Part (CIP)Application of three previously filed applications. These threeapplications are Ser. No. 10/698,620 filed on Nov. 1, 2003, Ser. No.10/699,140 filed on Nov. 1, 2003 now issued into U.S. Pat. No.6,862,127, and 10/699,143 filed on Nov. 1, 2003 now issued into U.S.Pat. No. 6,903,860 by the Applicant of this patent applications. Thedisclosures made in these patent applications are hereby incorporated byreference in this patent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to system configuration andmethod for controlling an image projection apparatus. More particularly,this invention relates to an image projection apparatus implemented withcoordinated control for turning on and off the light sourcecorresponding to the operation states of the mirror device performingthe function as a spatial light modulator.

2. Description of the Related Art

Even though there have been significant advances made in recent years inthe technologies of implementing electromechanical mirror devices asspatial light modulators (SLM), there are still limitations anddifficulties with displaying high quality images. Specifically, when thedisplay images are digitally controlled, the quality of the images isadversely affected because they are not displayed with a sufficientnumber of gray scales.

Electromechanical mirror devices have drawn considerable interestbecause of their application as spatial light modulators (SLM). Aspatial light modulator requires an array of a relatively large numberof micromirror devices. In general, the number of devices requiredranges from 60,000 to several millions for each SLM. Referring to FIG.1A for a digital video system 1 includes a display screen 2 disclosed ina relevant U.S. Pat. No. 5,214,420. A light source 10 is used togenerate light beams to project illumination for the display images onscreen 2. The light 9 projected from the light source is furtherconcentrated and directed toward lens 12 by way of mirror 11. Lenses 12,13 and 14 form a beam columnator operative to columnate the light 9 intoa column of light 8. A spatial light modulator (SLM) 15 selectivelyredirects a portion of the light from path 7 toward lens 5 to display onscreen 2 through data transmitted over data cable bus 18. FIG. 1B showsa SLM 15 that has a surface 16 that includes an array of switchablereflective elements 17, 27, 37, and 47, each of these reflectiveelements is attached to a hinge 30. When the element 17 is in an ONposition, a portion of the light from path 7 is reflected and redirectedalong path 6 to lens 5 where it is enlarged or spread along path 4 toimpinge on the display screen 2, forming an illuminated pixel 3. Whenthe element 17 is in an OFF position, the light is reflected away fromthe display screen 2, and, hence, pixel 3 is dark.

Each mirror element that constitutes a mirror device to function as aspatial light modulator (SLM) is comprised of a mirror and electrodes. Avoltage applied to the electrode(s) generates a coulomb force betweenthe mirror and the electrode(s), thereby making it possible to controland incline the mirror for deflection.

When a mirror is deflected by a voltage applied to the electrode(s), thedirection of the reflected incident light also changes. The direction ofthe reflected light is changed in accordance with the deflection angleof the mirror. When almost all of an incident light is reflected onto aprojection path designated for a display image, it is referred to as an“ON light”. When a light is not reflected to the designated projectionpath for the display image, it is referred to as an “OFF light”.

“Intermediate light” refers to the light reflected to a projection pathwith a smaller quantity of light than the ON light, and a ratio existsbetween the incident light reflected to a projection path (i.e., the ONlight) and that reflected from a projection path (i.e., the OFF light).According to the convention of present specification, a clockwise (CW)angle of rotation is positive (+) and a counterclockwise (CCW) angle ofrotation is negative (−). A deflection angle is defined as zero degree(0°) when the mirror is in the initial state.

The on-and-off states of the micromirror control scheme as thatimplemented in the U.S. Pat. No. 5,214,420, and in most conventionaldisplay systems, limit the quality of the display. Specifically,applying the conventional configuration of a control circuit limits thegray scale gradations produced in a conventional system (PWM between ONand OFF states), which is limited by the LSB (least significant bit, orthe least pulse width). Due to the ON-OFF states implemented in theconventional systems, there is no way of providing a shorter pulse widththan the duration represented by the LSB. The least quantity of light,which determines the gray scale, is the light reflected during the leastpulse width. The limited levels of gray scale lead to degradation of thedisplay image.

Specifically, FIG. 1C exemplifies, as related disclosures, a circuitdiagram for controlling a micromirror according to U.S. Pat. No.5,285,407. The control circuit includes memory cell 32. Varioustransistors are referred to as “M*” where “*” designates a transistornumber and each transistor is an insulated gate field effect transistor.Transistors M5 and M7 are p-channel transistors; transistors M6, M8, andM9 are n-channel transistors. The capacitances, C1 and C2, represent thecapacitive loads in the memory cell 32. The memory cell 32 includes anaccess switch transistor 9 and a latch 32 a, based on a Static RandomAccess Switch Memory (SRAM) design. All access transistors M9 on Rowline receive a DATA signal from Bit-line 31 a. The particular memorycell 32 is accessed for writing a bit to the cell by turning on theappropriate row select transistor M9, using the ROW signal functioningas a Word-line. Latch 32 a consists of two cross-coupled inverters,M5/M6 and M7/M8, which permit two stable states, that include a state 1when Node A is high and Node B is low, and state 2 when Node A is lowand Node B is high.

The mirror is driven by a voltage applied to the landing electrode, andis held at a predetermined deflection angle on the landing electrode. Anelastic “landing chip” is formed on the landing electrode, which putsthe landing electrode in contact with the mirror, and deflects themirror toward the opposite direction when the deflection of the mirroris switched. The landing chip has the same potential as the landingelectrode so as to prevent a possible short from the contact between thelanding electrode and the mirror.

Each mirror formed on a device substrate has a square or rectangularshape with a length of 4 to 15 um on each side. In this configuration, areflected light that is not purposefully applied for an image display isinadvertently generated by reflections through the gap between adjacentmirrors, which degrades the contrast of the image display. In order toovercome such problems, the mirrors are arranged on a singlesemiconductor wafer substrate with a layout that minimizes the gapsbetween the mirrors. One mirror device is generally designed to includean appropriate number of micromirrors wherein each one is manufacturedas a deflectable mirror on the substrate that displays a pixel of animage. The appropriate number of elements for a display image complieswith the display resolution standard according to VESA Standard definedby Video Electronics Standards Association or television broadcaststandards. The pitch between the mirrors of the mirror device is 10 μmand the diagonal length of the mirror array is about 0.6 inches when themirror device has a plurality of mirror elements corresponding to theWXGA (resolution: 1280 by 768) defined by VESA.

Switching between dual states, as illustrated by the control circuit inFIG. 1C, positions the micromirrors in an ON or an OFF angularorientation as shown in FIG. 1A. The brightness, i.e., the gray scalesof a digitally controlled image system is determined by the length oftime the micromirror stays in an ON position. The length of time amicromirror is in an ON position is controlled by a multiple bit word.FIG. 1D shows the “binary time intervals” when controlling micromirrorswith a four-bit word. As shown in FIG. 1D, the time durations haverelative values of 1, 2, 4, and 8 which in turn define the relativebrightness for each of the four bits, where the “1” is least significantbit (LSB) and the “8” is the most significant bit. According to thecontrol mechanism, the minimum controllable differences between grayscales for showing different levels of brightness are represented by the“least significant bit” that maintains the micromirror at an ONposition.

For example, assuming n bits of gray scales, one time frame is dividedinto 2^(n)−1 equal time periods. For a 16.7-millisecond frame period andn-bit intensity values, the time period is 16.7/(2^(n)−1) milliseconds.

Having established these times for each pixel of each frame, the pixelintensities are quantified such that black is 0 time period, 1 timeperiod is the intensity level represented by the LSB, and the maximumbrightness is 2^n−1 time periods.

Each pixel's quantified intensity determines its ON-time during a timeframe. Thus, during a time frame, each pixel with a quantified value ofmore than 0 is ON for the number of time periods that correspond to itsintensity. The viewer's eye integrates the pixel brightness so that theimage appears the same as if it were generated with analogous levels oflight.

For controlling deflectable mirror devices, the PWM applies data to beformatted into “bit-planes”, with each bit-plane corresponding to a bitweight of the quantity of light. Thus, if the brightness of each pixelis represented by an n-bit value, each frame of data has then-bit-planes. Then, each bit-plane has a 0 or 1 value for each displayelement. According to the PWM scheme as described in the precedingparagraphs, each bit-plane is separately loaded and the display elementsare controlled on the basis of bit-plane values corresponding to thevalue of each bit within one frame. For example, the bit-plane accordingto the LSB of each pixel is displayed as 1 time period.

When adjacent image pixels have very coarse gray scales caused bydifferences in brightness, artifacts become visible between theseadjacent image pixels, degrading the quality of the displayed image. Thedegradation of displayed image quality is especially pronounced in thebright areas of images where there are “bigger gaps” in the gray scale,i.e. brightness, between adjacent image pixels. These gaps are theresult of the digitally controlled image's inability to obtainsufficient brightness levels.

The mirrors are controlled at either the ON or OFF position. Then, thebrightness of a displayed image is defined by the length of time eachmirror remains at the ON position. In order to increase the levels ofbrightness, the switching speed of the ON and OFF positions for themirror is increased. Therefore, the digital control signals need ahigher number of bits. However, when the switching speed of the mirrordeflection is increased, a stronger hinge is needed to support themirror, and to sustain the required number ON and OFF positions for themirror deflection. Furthermore, in order to drive the mirrors' hingetoward the ON or OFF positions, the electrode requires a higher voltage.The higher voltage may be as high as thirty volts. The mirrors producedby the CMOS technology may not be suitable for such a high range ofvoltages, therefore requiring the use of the DMOS mirror devices. Toproduce the DMOS mirror and control the higher gray scale, a morecomplicated production process and larger device areas are required. Inorder to gain the benefits of a smaller image display apparatus, theaccuracy of gray scales and the range of the operable voltage have to besacrificed in conventional mirror controls.

There are many patents related to the control of quantity of light.These include U.S. Pat. Nos. 5,589,852, 6,232,963, 6,592,227, 6,648,476,and 6,819,064. There are further patents and patent applications relatedto different light sources. These include U.S. Pat. Nos. 5,442,414,6,036,318 and Application 20030147052. Also, The U.S. Pat. No. 6,746,123has disclosed particular polarized light sources that prevent the lossof light. However, these patents or patent applications do not providean effective solution for attaining a sufficient gray scale in thedigitally controlled image display system.

Furthermore, there are many patents related to a spatial lightmodulation that include the U.S. Pat. Nos. 2,025,143, 2,682,010,2,681,423, 4,087,810, 4,292,732, 4,405,209, 4,454,541, 4,592,628,4,767,192, 4,842,396, 4,907,862, 5,214,420, 5,287,096, 5,506,597, and5,489,952. There are additional patented disclosures related to theimage projection apparatuses. These patented disclosures include U.S.Pat. No. 5,214,420, U.S. Pat. No. 5,285,407, U.S. Pat. No. 5,589,852,U.S. Pat. No. 6,232,963, U.S. Pat. No. 6,592,227, U.S. Pat. No.6,648,476, U.S. Pat. No. 6,819,064, U.S. Pat. No. 5,442,414, U.S. Pat.No. 6,036,318, United States Patent Application 20030147052, U.S. Pat.No. 6,746,123, U.S. Pat. No. 2,025,143, U.S. Pat. No. 2,682,010, U.S.Pat. No. 2,681,423, U.S. Pat. No. 4,087,810, U.S. Pat. No. 4,292,732,U.S. Pat. No. 4,405,209, U.S. Pat. No. 4,454,541, U.S. Pat. No.4,592,628, U.S. Pat. No. 4,767,192, U.S. Pat. No. 4,842,396, U.S. Pat.No. 4,907,862, U.S. Pat. No. 5,214,420, U.S. Pat. No. 5,287,096, U.S.Pat. No. 5,506,597, and U.S. Pat. No. 5,489,952. However, theseinventions do not provide a direct solution to overcome theabove-discussed limitations and difficulties.

In view of the above problems, an invention has disclosed a method forcontrolling the deflection angle of the mirror to express higher grayscales of an image in US Patent Application 20050190429. According tothis method, the quantity of light obtained during the oscillationperiod of the mirror is about 25% to 37% of the emission light intensityfor a mirror that is controlled under a constant ON-state.

With this method there is no particular need to drive the mirror in highspeed, making it possible to obtain a high level of gradation with a lowspring constant in the spring member supporting the mirror, which allowsfor a reduction in drive voltage. A display image that uses the mirrordevice described above is broadly categorized into two types, i.e. asingle-plate equipped with only one spatial light modulator and amulti-plate equipped with a plurality of spatial light modulators. Inthe single-plate, changing colors in turn displays a color image, i.e.,the frequency or wavelength of projected light is changed by time. Inthe multi-plate, a color image is displayed when the spatial lightmodulators corresponding to different colored beams of light, i.e.frequencies or wavelengths of the light, modulate the beams of light;and are constantly combined with them.

Specifically, each micromirror device is separately controlled withinone frame or one sub-frame period. For example, it is possible tocontrol some mirrors under the ON light state for a longer period thanother mirrors. This differentiates the brightness of each mirror element(i.e., the product between the intensity of the ON light and the periodof the ON light state) during one frame or one sub-frame period.Separately controlling each mirror element causes each mirror to shiftfrom the deflection angle of the ON light state to that of the OFF lightstate in accordance with the period in which each mirror elementreflects the ON light.

Each mirror element that shifts when light is irradiated causes somemirror elements to reflect the light unstably, generating a blur inmotion images. Moreover, a continuous ON position for a light sourcethat is comprised in a projection apparatus that irradiates light ontothe mirror device heats it up, and increases power consumption.

SUMMARY OF THE INVENTION

In consideration of the above described problems, one aspect of thepresent invention is to remove the unstable reflection of incident lightcaused when each mirror element is shifted during one frame or sub-frame

A first exemplary embodiment of the present invention provides aprojection apparatus, includes a mirror device that includes a firstelectrode part and a second electrode part, an elastic hinge placedbetween the first electrode part and second electrode part, a mirrorthat is supported by the elastic hinge and that is deflected with afirst coulomb force generated between the mirror and first electrodepart and with a second coulomb force generated between the mirror andsecond electrode part; and a light source for emitting illuminationlight to be reflected by the mirror, wherein the light source suppressesthe emission of the illumination light during a period in which themirror performs a series of operations to shift from a non-deflectionstate, placing the mirror in a stationary and non-deflection state, to apredetermined deflection state.

A second exemplary embodiment of the present invention provides theprojection apparatus according to the first exemplary embodiment,wherein the electric potential at the first electrode part is the sameas the potential at the second electrode part.

A third exemplary embodiment of the present invention provides theprojection apparatus according to the second exemplary embodiment,wherein the first electrode part and the second electrode part form asingle drive electrode.

A fourth exemplary embodiment of the present invention provides theprojection apparatus according to the second exemplary embodiment,wherein the mirror includes the non-deflection state, a first deflectionstate in which the mirror is stationary in the state of being deflectedby the first coulomb force that is larger than the second coulomb force,and a second deflection state in which the mirror is stationary in thestate of being deflected by the second coulomb force that is larger thanthe first coulomb force, wherein the predetermined deflection state isthe second deflection state, wherein the first coulomb force is largerthan the second coulomb force if the electric potential is set higherthan the electric potential in the non-deflection state when the mirroris in the aforementioned non-deflection state.

A fifth exemplary embodiment of the present invention provides theprojection apparatus according to the fourth exemplary embodiment,wherein the area size of the surface of the first electrode part inwhich the first coulomb force is generated is larger than the area sizeof the surface of the second electrode part in which the second coulombforce is generated.

A sixth exemplary embodiment of the present invention provides theprojection apparatus according to the fourth exemplary embodiment,wherein the permittivity of the first electrode part is smaller thanthat of the second electrode part.

A seventh exemplary embodiment of the present invention provides theprojection apparatus according to the fourth exemplary embodiment,wherein the series of operations is an operation for shifting to thesecond deflection state after shifting to the first deflection.

A eighth exemplary embodiment of the present invention provides theprojection apparatus according to the first exemplary embodiment,wherein the mirror device further comprises a main power supply, whereinthe series of operations is carried out after the main power supply isturned on.

A ninth exemplary embodiment of the present invention provides theprojection apparatus according to the first exemplary embodiment,wherein the mirror device is controlled with externally inputted imagedata, and the series of operations is carried out after completingdisplay of each frame of the image data.

A tenth exemplary embodiment of the present invention provides theprojection apparatus according to the first exemplary embodiment,wherein the light source suppresses the emission of the illuminationlight during a period in which the mirror performs the series ofoperations.

An eleventh exemplary embodiment of the present invention provides acontrol method used for a projection apparatus includes a mirror devicefor which the deflection state that a mirror can be deflected to from anon-deflection state in which the mirror is not deflected is limited toa specific deflection state that is different from a desired deflectionstate, and a light source for emitting illumination light to bereflected by the mirror device, includes: suppressing the illuminationlight emitted from the light source or maintaining the suppressed statein the non-deflection state; deflecting the mirror to place it in thespecific deflection state; deflecting the mirror to place it in thedesired deflection state; maintaining the mirror in the desireddeflection state; and emitting the illumination light from the lightsource.

A twelfth exemplary embodiment of the present invention provides acontrol method used for a projection apparatus includes (i) and (ii),where (i) is a mirror device which includes a mirror, first and secondelectrode parts and an elastic hinge that is placed between the firstand second electrode parts and that supports the mirror and for whichthe deflection state that a mirror can be deflected to from anon-deflection state in which the mirror is not deflected is limited toa specific deflection state that is different from a desired deflectionstate, and (ii) is a light source for emitting illumination light to bereflected by the mirror device, includes: suppressing the illuminationlight emitted from the light source or maintaining the suppressed statein the non-deflection state; applying a voltage to the first electrodeand second electrode to deflect the mirror with the difference between afirst coulomb force and a second coulomb force that is larger than thefirst coulomb force, where the first coulomb force is generated betweenthe first electrode and the mirror, and the second coulomb force isgenerated between the second electrode and the present mirror, andthereby the mirror is put in the specific deflection state; eliminatingthe voltage to shift the mirror toward the desired deflection state bymeans of the restoring force of the elastic hinge; applying the voltageto put the mirror in the desired deflection state when the first coulombforce becomes larger than the second coulomb force as a result ofapplying the voltage; maintaining the mirror in the desired deflectionstate by continuing the application of the voltage; and emitting theillumination light from the light source.

A thirteenth exemplary embodiment of the present invention provides thecontrol method used for a projection apparatus according to the twelfthexemplary embodiment, wherein the voltage applied to the first electrodeis equal to the voltage applied to the second electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below with reference to thefollowing Figures.

FIG. 1A is a functional block diagram showing the configuration of aprojection apparatus according to a conventional technique.

FIG. 1B is a top view for showing the configuration of a mirror elementof the projection apparatus according to a conventional technique.

FIG. 1C is a circuit diagram for showing the circuit configuration ofthe drive circuit of a mirror element of the projection apparatusaccording to a conventional technique.

FIG. 1D is a timing diagram for showing the mirror control time schemesaccording to the image format used in a projection apparatus accordingto a conventional technique.

FIG. 2A is a cross sectional view for showing the relationship betweenthe numerical aperture NA1 of an illumination light path, the numericalaperture NA2 of a projection light path, and the tilt angle α of amirror.

FIG. 2B is a diagram for illustrating the etendue in the case of using adischarge lamp light source and projecting an image by way of an opticaldevice.

FIG. 3 is a functional block diagram for showing the configuration of aprojection apparatus according to a preferred embodiment of the presentinvention.

FIG. 4 is a functional block diagram showing the configuration of amulti-panel projection apparatus according to another preferredembodiment of the present invention.

FIG. 5A is a block diagram for illustrating the configuration of acontrol unit comprising a single-panel projection apparatus according toa preferred embodiment of the present invention.

FIG. 5B is a side view for showing the configuration of anothermedication of a multi-panel projection apparatus according to apreferred embodiment of the present invention.

FIG. 6A is a block diagram illustrating the configuration of the lightsource drive circuit of a projection apparatus according to a preferredembodiment of the present invention.

FIG. 6B is a block diagram for illustrating a modification of theconfiguration of the light source drive circuit of a projectionapparatus according to a preferred embodiment of the present invention.

FIG. 7 is a diagram showing the relationship between the applied currentand the emission light intensity of a light source drive circuit in theembodiment of the present invention;

FIG. 8 is a diagram for showing the relationship between the emissionlight intensity and the current applied to the light source drivecircuit according to the embodiment of the present invention;

FIG. 9 is a schematic diagram for illustrating the layout of theinternal configuration of a spatial light modulator according to theembodiment of the present invention;

FIG. 10 is a cross-sectional diagram of an individual pixel unitconstituting a spatial light modulator according to the embodiment ofthe present invention;

FIG. 11 is a side cross sectional diagram for illustrating theconfiguration of an individual pixel unit constituting a spatial lightmodulator according to the embodiment of the present invention.

FIG. 12 is a chart illustrating a conversion from binary data tonon-binary data performed in a projection apparatus according to theembodiment of the present invention.

FIG. 13 is a chart illustrating a conversion from binary data tonon-binary data performed in a projection apparatus according to theembodiment of the present invention.

FIG. 14 is a chart for showing a conversion from binary data tonon-binary data performed in a projection apparatus according to theembodiment of the present invention.

FIG. 15 is a chart for illustrating a conversion from binary data tonon-binary data performed in a projection apparatus according to theembodiment of the present invention.

FIG. 16 is a graph illustrating a synchronism between the deflectionangle of an individual mirror and the light source in the embodiment ofthe present invention;

FIG. 17 is a graph illustrating an individual mirror element performingone OFF operation within one frame while synchronizing a light sourceand the individual mirror element in the embodiment of the presentinvention.

FIG. 18A shows the configuration, in the initial state, of one mirrorelement according to a preferred embodiment of the present invention.

FIG. 18B shows the configuration, in an ON state, of one mirror elementaccording to a preferred embodiment of the present invention.

FIG. 18C shows the configuration, in an OFF state, of one mirror elementaccording to a preferred embodiment of the present invention.

FIG. 18D shows the configuration, in a free oscillation state, of onemirror element according to a preferred embodiment of the presentinvention.

FIG. 18E is a block diagram showing an exemplary configuration of onemirror element according to a preferred embodiment of the presentinvention.

FIG. 19 is a diagram showing the configuration using a material withdifferent permittivity on the upper parts of the first electrode partand second electrode part of a single address electrode of one mirrorelement according the embodiment of the present invention.

FIG. 20 is a graph illustrating that a light source is turned off insynchronous with a dummy operation of an individual mirror elementaccording the embodiment of the present invention.

FIG. 21 is a graph illustrating a synchronism between the deflectionangle of an individual mirror element and a light source according tothe embodiment of the present invention.

FIG. 22 is a graph illustrating a synchronism among the deflection angleof an individual mirror element, an address electrode and a light sourceaccording to the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[Outline of the Device]

The following description is for a mirror device implemented as aspatial light modulator (SLM) in an image projection apparatus. It iswidely known to implement different kinds of spatial light modulators(SLM), such as a transmissive liquid crystal, a reflective liquidcrystal, a mirror array, etc. in the image projection apparatuses.

A spatial light modulator (SLM) includes a two-dimensional array thatarranges, enlarges, and then displays on a screen by way of a projectionlens arrayed as tens of thousands to millions of miniature modulationelements for projecting individual pixels corresponding to an image.

Generally, there are primarily two types of spatial light modulatorsimplemented in the projection apparatuses. These two types are: 1) aliquid crystal device for modulating the polarizing direction ofincident light by applying a control voltage to the liquid crystalsealed between transparent substrates, and 2) a mirror device thatdeflects miniature micro electro mechanical systems (MEMS) mirrors withelectrostatic force and controls the reflecting direction ofillumination light.

[Outlines of Mirror Size and Resolution]

Next is an outline description of the size of a mirror and theresolution.

The size of the MEMS mirrors for a mirror device is between 4 μm and 10μm on each side. The mirrors are placed on a single semiconductor wafersubstrate and arranged according to a configuration to minimize the gapbetween adjacent mirrors to prevent excess reflected light from the gapfor reducing the degradation of the contrast for a modulated image. Themirror device for an image display apparatus comprises appropriatenumber of mirror elements to function as the image display elements. Theappropriate number of image display elements will be determined incompliance with the resolution specified by the Video ElectronicsStandards Association (VESA) and the television Broadcasting standard.In the case of a mirror device comprising the number of mirror elementscompliant to the WXGA (with the resolution of 1280×768) specified by theVESA, and in which mirrors are arrayed in intervals (noted as “pitch”hereinafter) of 10 μm, a sufficiently miniature mirror device isconfigured with about 15.49 mm (0.61 inches) of the diagonal length ofthe display area.

[Outline of Projection Apparatus]

Next is an outline description of the configuration of a projectionapparatus.

There are primarily two types of deflection-type (“deflectable”) lightmodulators implemented in the projection apparatuses. These two typesare: 1) a single-panel projection apparatus that comprises a singlespatial light modulator, changing the frequency of a projection light intime series and displaying an image in colors, and 2) a multi-panelprojection apparatus that comprises a plurality of spatial lightmodulators, modulating an illumination light with different frequenciesconstantly by means of the individual spatial light modulators anddisplaying an image in colors by synthesizing these modulated lights.

[Outline of the Introduction of Laser Light Source]

Here follows an introductory description of a laser light source. Thereis a close relationship among the numerical aperture (NA) NA1 of anillumination light path, the numerical aperture NA2 of a projectionlight path, and the tilt angle α of a mirror in the projection apparatusimplemented with the above-described mirror device as a reflectivespatial light modulator. FIG. 2A shows the relationship between theseparameters.

For the discussion of the exemplary embodiment, it is assumed that thetilt angle α of a mirror 1011 is 12 degrees. When a modulated lightreflected by the mirror 1011 and incident to the pupil of the projectionlight path is set perpendicular to the device substrate 1012, theillumination light is incident from a direction inclined by 2α, that is,24 degrees, relative to the perpendicular of the device substrate 1012.In order to most efficiently project the light beam reflected by themirror to the pupil of the projection lens, it is desirable that thenumerical aperture of the projection light path be equal to thenumerical aperture of the illumination light path. If the numericalaperture of the projection light path is smaller than that of theillumination light path, the illumination light cannot be sufficientlyimported into the projection light path; if the numerical aperture ofthe projection light path is larger that that of the illumination lightpath, the illumination light can be entirely transmitted. In the lattercase, the projection lens then becomes unnecessarily large, which makesconfiguring the projection apparatus inconvenient. Furthermore, thelight fluxes of the illumination light and projection light must beseparate because the optical members of the illumination system andthose of the projection system must be kept separate. With the aboveconsiderations in mind, when a spatial light modulator with mirror tiltangle of 12 degrees is used, the numerical aperture (NA) NA1 of theillumination light path and the numerical aperture NA2 of the projectionlight path are preferred to be set as follows:NA1=NA2=sin α=sin 12°Let F1 be the aperture number of the illumination light path and F2 bethe aperture number of the projection light path, then the numericalaperture can be converted a product of F as follows:F1=F2=1/(2*NA)=1/(2*sin 12°)=2.4

In order to maximize the projection of the illumination light emittedfrom a light source possessing non-directivity in the direction of theemitted light such as a high-pressure mercury lamp or a xenon lamp,which are generally used for projection apparatuses, the angle of lightprojecting on the illumination light path must be maximized. Since thenumerical aperture of the illumination light path is determined by thespecification by the tilt angle of a mirror, the tilt angle of themirror needs to be large in order to increase the numerical aperture ofthe illumination light path.

Increasing the deflection angle of mirror, however, increases the drivevoltage for the mirror. To increase the deflection angle of mirror, along distance between the mirror and a driving electrode is required,because it is necessary to secure a physical space to tilt the mirror.It is possible to increase the drive voltage to compensate for thedecrease in the drive force due to an increase in distance. However, thedrive voltage is conventionally about 5 to 10 volts in a drive circuitof a CMOS process used for driving a mirror and, therefore, a relativelyspecial process, such as a DMOS process, is required if a drive voltagein excess of about 10 volts and that would significantly increase theproduction costs.

On the other hand, for the purposes of cost reduction, it is desirableto obtain as many mirror devices as possible from a single semiconductorwafer substrate, since this would be an improvement of productivity.That is, a reduction of the pitch between mirror elements reduces thesize of the mirror device. A decrease in mirror size results in areduction in the area of the electrode, which, in turn, requires lowerdriving power.

In contrast, a mirror device is able to produce brighter illuminationonly if a conventional lamp is used. Yet the usage of a conventionallamp with a non-directivity in its emission substantially reduces theefficiency of light usage. This is attributable to a relationshipcommonly called entendue. FIG. 2B is an illustrative diagram fordescribing etendue by illustrating the use of an arc discharge lamplight source and projecting an image by way of an optical device.

As shown in FIG. 2B, “y” is the size of a light source 4150, and “u” isthe importing angle of light on the light source side. Further, “u′” isthe converging angle on the image side, and “y′” is the size of theimage of a light source, the relationship among these is represented bythe following equation:y*u=y′*u′

The above equation shows that the smaller the device on which a lightsource is intended to be imaged, the smaller the importing angle on thelight source becomes. This is why it is advantageous to use a laserlight source, wherein emission light possesses strong directivity, inorder to allow for a decrease in mirror size.

[Outline of Oscillation Control]

Here follows a description of an oscillation control.

Another method for reducing the drive voltage, other than minimizing thetilt angle of a mirror, is disclosed in US Patent Application20050190429. According to this method, a mirror is put into freeoscillation in the inherent oscillation frequency, and the intensity oflight during the oscillation period of the mirror is thereby reduced toabout 25% to 37% of the emission light intensity for a mirror that iscontrolled under a constant ON-state.

According to this method, there is no particular need to drive themirror in high speed, making it possible to obtain a high level ofgradation with a low spring constant in the spring member supporting themirror, which allows for a reduction in the drive voltage.

As described above, the adoption of a light source with directivity,such as a laser light source, makes it possible to reduce the deflectionangle of a mirror and the size of the mirror device without decreasingthe brightness of the light source. Furthermore, such a light sourceimproves gradation without requiring an increase drive voltage ifemployed with the above described oscillation control.

However, the space usage efficiency of an electrode can be degraded ifthe electrode of a driving mirror and stopper, which defines thedeflection angle of the mirror, is individually configured as in theconventional method. U.S. Pat. No. (“USP” hereinafter) 5,583,688, USPApplication 20060152690, U.S. Pat. No. 6,198,180 or U.S. Pat. No.6,992,810 have disclosed a structure for regulating the modulation angleof a mirror of a conventional mirror device. Any of the disclosedexamples have a structure that faces the difficulty of increasing thesize of an address electrode.

Embodiment 1

The following is a description, in detail, of the preferred embodimentof the present invention with reference to the accompanying drawings.

FIG. 3 is a functional block diagram for showing the configuration of aprojection apparatus according to a preferred embodiment of the presentinvention.

A projection apparatus 5010 according to the present embodimentcomprises a single spatial light modulator (SLM) 5100, a control unit5500, a Total Internal Reflection (TIR) prism 5300, a projection opticalsystem 5400 and a light source optical system 5200 as exemplified inFIG. 3. The projection apparatus 5010 is a single-panel projectionapparatus 5010 comprising a single spatial light modulator 5100. Theprojection optical system 5400 is implemented with the spatial lightmodulator 5100 and a TIR prism 5300 in the optical axis of theprojection optical system 5400, The projection optical system 5400further includes a light source optical system 5200 with a mutuallyaligned optical axis.

The TIR prism 5300 receives an illumination light 5600 transmitted fromthe light source optical system 5200 to project the light to the spatiallight modulator 5100 at a prescribed inclination angle as an incidentlight 5601. The SLM 5100 reflects a reflection light 5602 to transmit tothe projection optical system 5400. The projection optical system 5400projects the reflection light 5602 transmitted from the spatial lightmodulator 5100 and TIR prism 5300 onto a screen 5900 as projection light5603. The light source optical system 5200 comprises a adjustable lightsource 5210 for generating the illumination light 5600, a condenser lens5220 for focusing the illumination light 5600, a rod type condenser body5230 and a condenser lens 5240. The adjustable light source 5210,condenser lens 5220, rod type condenser body 5230 and condenser lens5240 are arranged in the aforementioned order on the optical axis of theillumination light 5600, which is emitted from the variable light source5210 and incident to the side face of the TIR prism 5300. The projectionapparatus 5010 employs a single spatial light modulator 5100 forprojecting a color image display on the screen 5900 by applying a colorsequential image display technology. Specifically, the adjustable lightsource 5210, includes a red laser light source 5211, a green laser lightsource 5212, and a blue laser light source 5213 which are notspecifically shown in FIG. 3. The adjustable light source allowsindependent controls for light emission states by dividing one frame ofdisplay data into sub-fields (i.e., three sub-fields, that is, red (R),green (G) and blue (B) in the present case) and causes the red laserlight source 5211, the green laser light source 5212, and the blue laserlight source 5213 each to emit their respective light during the timeperiod corresponding to the sub-field of each color as described later.

FIG. 4 is a functional block diagram for showing a modification of theconfiguration of a projection apparatus according to the presentinvention. The projection apparatus 5020 is generally referred to as amultiple-plate projection apparatus comprising a plurality of spatiallight modulators 5100, which is different from the above-describedprojection apparatus 5010. Furthermore, the projection apparatus 5020comprises a control unit 5502 instead of the control unit 5500. Theprojection apparatus 5020 comprises spatial light modulators 5100, andfurther includes a light separation/synthesis optical system 5310disposed between the projection optical system 5400 and each of thespatial light modulators 5100. The light separation/synthesis opticalsystem 5310 further includes a TIR prism 5311, a prism 5312 and a prism5313. The TIR prism 5311 has the function of directing the incidentillumination light 5600 from the side of the optical axis of theprojection optical system 5400 to the spatial light modulator 5100 asincident light 5601. The prism 5312 carries out the functions 1) ofseparating red (R) light from an incident light 5601 incident by way ofthe TIR prism 5311 and making the red light incident to the redlight-use spatial light modulator 5100, and 2) directing the reflectionlight 5602 of the red light to the TIR prism 5311.

Likewise, the prism 5313 carried out the functions of 1) separating blue(B) and green (G) lights from the incident light 5601 incident by way ofthe TIR prism 5311 and projecting to the blue color spatial lightmodulators 5100, and 2) directing the reflection light 5602 of the greenlight and blue light to the TIR prism 5311.

Therefore, three spatial light modulators 5100 simultaneously modulatelight of three colors of R, G and B and the resultant reflection lightswith respective modulations are projected onto the screen 5900 as theprojection light 5603 by way of the projection optical system 5400, andthus a color display is achieved. Note that various modifications arepossible for a light separation/synthesis optical system as lightseparation/synthesis optical system 5310.

FIG. 5A is a block diagram for showing the configuration of the controlunit 5500 as that implemented in the above described single-panelprojection apparatus 5010. The control unit 5500 comprises a framememory 5520, an SLM controller 5530, a sequencer 5540, a light sourcecontrol unit 5560, and a light source drive circuit 5570. The sequencer5540 comprises a microprocessor that controls operation timing and thecontrol unit 5500 and spatial light modulators 5100. The frame memory5520 retains one frame of digital video data input 5700 received from anexternal device (not shown in FIG. 5A), which is connected to a videosignal input unit 5510. The digital video data input 5700 is updated,every time the display of one frame is completed. The SLM controller5530 processes the digital video data input 5700 read from the framememory 5520 as described later, separates the read data into sub-fields5701 through 5703, and outputs the data to the spatial light modulators5100 as binary data 5704 and non-binary data 5705, which are used forimplementing an the ON/OFF control and oscillation control (which aredescribed later) of a mirror 5112 of the spatial light modulator 5100.The binary data 5704 contains a pulse width in accordance with theweighing value of an individual bit. The non-binary data 5705 convertedfrom the digital video data input 5700 becomes a bit string thatincludes continuous bits of “1” corresponding to the level ofbrightness, and in this bit stream of the non-binary data 5705 has thesame weighting factor (e.g., “1”). The sequencer 5540 outputs a timingsignal to the spatial light modulator 5100 synchronously with thegeneration of the binary data 5704 and non-binary data 5705 at the SLMcontroller 5530. The video image analysis unit 5550 outputs a videoimage analysis signal 5800 used for generating various light sourcepatterns (which are described later) on the basis of the input digitalvideo data 5700 received from the video signal input unit 5510. Thelight source control unit 5560 controls the operation of the variablelight source 5210 by using a light source profile control signal tocontrol the light source drive circuit 5570 for emitting theillumination light 5600. This light source profile control signal isgenerated from the video image analysis signal 5800 on the basis of theinput of the video image analysis signal 5800 inputted from the videoimage analysis unit 5550 by way of the sequencer 5540 and generateslight source pulse patterns. The light source drive circuit 5570 drivesthe red laser light source 5211, green laser light source 5212, and bluelaser light source 5213 of the variable light source 5210 to emit lightaccording to the light source pulse patterns received from the lightsource control unit 5560. The present embodiment illustrates the use ofa laser light source; an alternative configuration may use asemiconductor light source that arrays light emitting diodes (LEDs) orthe like.

The configuration shows the light source drive circuit 5570 drives andflexibly adjusts the laser light sources of the respective colors. Analternative configuration may be such that the light source drives thered laser light source 5211, green laser light source 5212 and bluelaser light source 5213, respectively.

A configuration such that the adjustable light source 5210 comprises thered laser light source 5211, green laser light source 5212 and bluelaser light source 5213 and each of these laser light sources isflexibly adjustable. An alternative configuration may be such that theadjustable light source 5210 is a single light source capable ofemitting light containing all wavelengths corresponding to therespective colors of at least red (R), green (G) and blue (B).

FIG. 5B is a block diagram for showing the configuration of the controlunit of a multi-panel projection apparatus according to the presentembodiment. The control unit 5502 comprises SLM controllers 5531, 5532and 5533, which are used for controlling, respectively, the spatiallight modulators 5100 for modulating the colors R, G and B, and theplacement of the controllers is different from the above describedcontrol unit 5500, which is otherwise similar. Specifically, the SLMcontroller 5531, SLM controller 5532 and SLM controller 5533corresponding to their respective color-use spatial light modulators5100 are formed on the same substrates as those of the respectivespatial light modulators 5100. This configuration makes it possible toplace the spatial light modulators 5100 and the corresponding SLMcontroller (5531, 5532 and 5533) close to each other, thereby enabling ahigh speed data transfer rate. Further, a system bus 5580 connects theframe memory 5520, light source control unit 5560, sequencer 5540 andSLM controllers 5531 through 5533, in order to speed up and simplify theconnection path of each connecting element.

The configuration shows a single light source drive circuit 5570 thatflexibly controls and drives the laser light sources of the respectivecolors. An alternative configuration may include independent lightsource drive circuit to flexibly control and drive the red laser lightsource 5211, green laser light source 5212 and blue laser light source5213, respectively.

The configuration illustrates adjustable a light source 5210 thatincludes flexibly adjustable red laser light source 5211, green laserlight source 5212 and blue laser light source 5213. An alternativeconfiguration may include adjustable light source 5210 implemented witha single light source for emitting light containing all wavelengthscorresponding to the respective colors of at least red (R), green (G)and blue (B). This configuration makes it possible for a single chip SLMcontroller 5530 to control the spatial light modulators 5100, therebyreducing the size of the apparatus

FIG. 6A is a schematic circuit diagram for illustrating theconfiguration of the light source drive circuit 5570 (i.e., the lightsource drive circuits 5571, 5572 and 5573) according to the presentembodiment. The light source drive circuit as depicted in FIG. 6Acomprises a plurality of constant current circuits 5570 a (i.e., I (R,G, B), through I (R, G, B)_(n)) which correspond to switching circuits5570 b (i.e., switching circuits SW (R, G, B)₁ through SW (R, G,B)_(n)), in order to obtain the desired light intensities of emission P₁through P_(n) for the variable light sources 5210 (i.e., the red laserlight source 5211, green laser light source 5212 and blue laser lightsource 5213).

The switching circuit 5570 b switches the variable light source 5210,i.e., red laser light source 5211, green laser light source 5212 andblue laser light source 5213, in accordance with the desired emissionprofile of the adjustable light source 5210. The initial values of theoutput current of the constant current circuits 5570 a (i.e., constantcurrent circuits I (R, G, B)_(n)), when the gray scale of the emissionintensity of the variable light source 5210 is designated at N bits(where N≧n), are as follows:I(R,G,B)₁ =I _(th)+LSBI(R,G,B)₂=LSB+1I(R,G,B)₃=LSB+2. . .. . .I(R,G,B)_(n) =MSB

This is an example of a gray scale display based on emission intensity.A similar gray scale display is achievable even if the emission period(i.e., an emission pulse width), emission interval (i.e., an emissioncycle), is flexibly controllable.

The relationship between the emission intensity of the adjustable lightsource and drive current for each color in this case is as follows. Notethat “k” is an emission efficiency corresponding to the drive current:P ₁ =k*(I _(th) +I ₁)P ₂ =k*(I ^(th) +I ₁ +I ₂). . .. . .P _(n) =k*(I _(th) +I ₁ +I ₂ + . . .+I _(n-1) +I _(n))

FIG. 6B is a schematic circuit diagram for showing an alternativeconfiguration of the light source drive circuit as another exemplaryembodiment of this invention. FIG. 6B, shows the constant currentcircuits 5570 a (I (R, G, B)₁ through I (R, G, B)_(n)) as constantcurrent circuits 5570 a (I₁ through I_(n)) and the switching circuits5570 b (SW (R, G, B), through SW (R, G, B)_(n)) as switching circuits5570 b (SW₁ through SW_(n)). As will be described below, the lightsource drive circuits 5570 according to the present embodiment isconfigured to make the individual constant current circuit 5570 a (i.e.,I (R, G, B)₁ in this case) to supply a bias current value equivalent tothe threshold current I_(th) of the variable light source 5210, or closeto the threshold current when a single semiconductor laser is used asthe variable light source 5210. This is because a high speed currentdrive is required to stabilize the switching operation of the lightsource drive circuits 5570 of the present embodiment and also to enablea high speed emission.

FIG. 6B shows the light source drive circuits 5570, i.e., the lightsource drive circuit 5571, light source drive circuit 5572, light sourcedrive circuit 5573 comprises bias current circuits 5570 c connected tothe variable light source 5210. The light source 5210 includes the redlaser light source 5211, green laser light source 5212 and blue laserlight source 5213 applied with a bias current I_(b), in addition to theconstant current circuits 5570 a. Furthermore, the constant currentcircuits 5570 a are connected to the variable light source 5210 througha high speed switching circuit 5570 d (SW_(pulse)) disposed on thedownstream side of the switching circuits 5570 b. According to theconfiguration shown in FIG. 6B, the relationship between the emissionintensity P_(n) and drive current of the variable light source for eachwavelength is as follows, where “k” is the emission intensity in termsof drive current:P _(b) =k*I _(b)(I _(b) ≈I _(th))P ₁ =k*(I _(th) +I ₁)P ₂ =k*(I _(th) +I ₁ +I ₂). . .. . .P _(n) =k*(I _(th) +I ₁ +I ₂ + . . .+I _(n-1) +I _(n))

Therefore, the relationship between each switching operation andemission output is as follows:SW _(pulse)=OFF:P _(b) =k*I _(b)≈0[mW] (where I _(b) ≈I _(th))SW ₁ :P ₁ =k*(I _(b) +I ₁)SW ₂ :P ₂ =k*(I _(b) +I ₁ +I ₂). . .. . .SW _(n) :P _(n) =k*(I _(b) +I ₁ +I ₂ + . . .I _(n-1) +I _(n))This makes it possible to attain an emission profile with an emissionintensity P_(b) that is nearly zero. The use of the switching circuits5570 d illustrated in FIG. 6B makes it possible to implement a circuitoperation unaffected by a drive current switching over caused by theswitching circuits 5570 b (SW₁ through SW_(n)) which are connected tothe respective constant current circuits 5570 a. Better image qualitymay be achieved if the switching circuits 5570 b (SW₁ through SW_(n))are switched over when the adjustable light source (i.e., the adjustablelight source 5210) is not emitting light.

The configuration shown in FIG. 6B is provided with a fixed currentvalue for the bias current value. It can alternatively be configured,however, with variable bias current by connecting the constant circuit5570 c to the light source control circuit 5560, so that the biascurrent is flexibly adjusted by the light source control circuit 5560 aswill be further explained below.

FIG. 7 is a chart showing the relationship between the applied current Iof the light source drive circuit shown in the above described FIG. 6Aand the emission intensity P_(n). FIG. 8 is a chart showing therelationship between the applied current I of the constant currentcircuit 5570 a of the light source drive circuit shown in FIG. 6B andemission intensity P_(b), emission intensity P_(n). Note that thedescription for FIGS. 6A and 6B assume that the changes in the emissionprofiles of the adjustable light source for each sub-frame correspond toeach gray scale bit. The display gray scale function of the spatiallight modulator 5100 is used, the number of required levels ofelectrical current decreases, reducing the numbers of constant currentcircuits 5570 a and switching circuits 5570 b needed and making itpossible to obtain the number of gray scales equal to, or higher than,the displayable gray scales of the spatial light modulator 5100.

FIG. 9 is a schematic circuit diagram for illustrating the layout of theinternal configuration of the spatial light modulator 5100 according tothe present embodiment. FIG. 10 is a cross-sectional diagram of anindividual pixel unit constituting the spatial light modulator 5100according to the present embodiment. FIG. 11 is a side cross sectionalview for illustrating the individual pixel unit comprising the spatiallight modulator 5100 according to the present embodiment.

As illustrated in FIG. 9, the spatial light modulator 5100 comprises amirror element array 5110, column drivers 5120, ROW line decoders 5130and an external interface unit 5140. The external interface unit 5140includes a timing controller 5141 and a selector 5142. The timingcontroller 5141 controls the ROW line decoder 5130 based on a timingsignal from the SLM controller 5530. The selector 5142 supplies thecolumn driver 5120 with digital signal from the SLM controller 5530. Inthe mirror element array 5110, the mirror elements are positioned whereindividual bit lines 5121, which extend vertically from the columndrivers 5120, cross individual word lines 5131. The word lines 5131extend horizontally from ROW decoders 5130.

As exemplified in FIG. 10, the individual mirror element 5112 tiltsfreely while supported by a hinge 5113 on substrate 5114. The mirror5112 is covered with a cover glass 5150 for protection. An OFF electrode5116 (and an OFF stopper 5116 a) and an ON electrode 5115 (and an ONstopper 5115 a) are formed symmetrically across the hinge 5113 on thesubstrate 5114. The OFF electrode 5116 draws the mirror 5112 with aCoulomb force by applying a predetermined voltage and tilts the mirror5112 to contact with the OFF stopper 5116 a. This causes the incidentlight 5601 projected to the mirror 5112 to reflect to the light path ofalone an OFF direction away from the optical axis of the projectionoptical system 5400.

The ON electrode 5115 draws the mirror 5112 with a Coulomb force byapplying a predetermined voltage and tilts the mirror 5112 to contactwith the ON stopper 5115 a. This causes the incident light 5601 incidentto the mirror 5112 to reflect to the light path along an ON directionmatching the optical axis of the projection optical system 5400.

A configuration that retains mirror 5112 by abutting the ON stopper 5115a or OFF stopper 5116 a is one among several optional arrangements. Analternative configuration may eliminate the ON stopper 5115 a or OFFstopper 5116 a, thereby maintaining mirror 5112 by abutting the ONelectrode 5115 or OFF electrode 5116.

As illustrated in FIG. 11, an OFF capacitor 5116 b is connected to theOFF electrode 5116, and the OFF capacitor 5116 b is connected to a bitline 5121-1 and a word line 5131 by way of a gate transistor 5116 c.Furthermore, an ON capacitor 5115 b is connected to the ON electrode5115, and the ON capacitor 5115 b is connected a bit line 5121-2 and aword line 5131 by way of a gate transistor 5115 c. The signals receivedon the word line 5131 control the turning on and off of the transistors5116 c and 5115 c. More specifically, the mirror elements 5111, whichare on one horizontal row in line with an arbitrary word line 5131, aresimultaneously selected, and the charging and discharging of the OFFcapacitor 5116 b and ON capacitor 5115 b are controlled by bit lines5121-1 and 5121-2, respectively. Thus, the ON and OFF states of themirrors 5112 of the individual mirror elements are controlled.

Embodiment 2

A projection apparatus according to the present embodiment comprises amirror device with mirror elements for modulating the incident lightemitted from the light source and turns the reflection of the incidentlight to the ON state to direct it to a projection path or to the OFFstate, so it is not directed to a projection path. Furthermore, thelight source and mirror device are controlled by a pulse widthmodulation (PWM) in either a frame or a sub-frame. Within the time themirror of maximum brightness (i.e., intensity of reflection light towardthe projection path) reflects the incident light to the ON state, theother mirrors are no longer ON. Outside of that time, the light isturned off within one frame or sub-frame.

A sub-frame is defined as a piece of data assigned to each color, i.e.,a light with specific wavelength when a plurality of incident lights isprojected with different wavelengths for displaying different colors insequence.

It is possible for a light source to be either a laser or a lightemitting diode (LED), which are both capable of performing pulseemission. The pulse emission-capable light source enablessynchronization with the mirror device. The mirror device is configuredby arraying a plurality of mirror elements comprising both a deflectablemirror, which is supported by an elastic hinge formed on a substratethat reflects the incident light from the light source, and an addresselectrode placed on the substrate and under the mirror, as describedabove in FIGS. 10 and 11. Note that it is preferable to control themirrors of the mirror device with non-binary data obtained by convertingthe binary data as shown in FIGS. 12, 13, 14 and 15.

The binary data 7704, comprising the 8-bit “10101010”, generates thenon-binary data 7705, which is a bit string that has equal weight foreach digit, as illustrated in FIG. 12. A control turns ON the mirror5112 for the period in which the bit string is continuous. Asillustrated in FIG. 12, the non-binary data 7705 is converted so thatthe bit string is within the display period of one frame, and turns ONthe mirror 5112 for a predetermined period in accordance with the bitstring number from the beginning of a frame display period.

As shown in FIG. 13, an 8-bit “01011010” binary data 7704 is convertedinto non-binary data 7705, which is a forward-packed bit string. FIG. 14illustrates a data string structure that converts the binary data 7704shown in FIG. 12, as described above, into a bit string of non-binarydata 7705 with the digits packed backward. In this case, the mirror 5112is turned ON only in the period of time corresponding to the bit stringnumber starting from the middle of a frame display period to the end.

Likewise, FIG. 15 illustrates another data string structure thatconverts the binary data 7704 shown in FIG. 13, as described above, intoa bit string of non-binary data 7705 with the digits packed backward,and controls the ON/OFF of the mirror 5112. When the ON/OFF iscontrolled by the non-binary data 7705, as described above, the ONperiod of the mirror 5112 becomes continuous, therefore controlling theemission intensity of the variable light source 5210 synchronously withthe ON period becomes easy.

Within the time period each mirror producing maximum brightness reflectsthe incident light to the ON position, the other mirrors finish the ONoperation. Beyond the time period, the mirror producing maximumbrightness performs the ON operation, turning the light source offwithin one frame or sub-frame. It is assumed that each mirror element isunder a PWM control that uses non-binary data. FIG. 16 is a graphshowing the synchronization between a light source and the deflectionangle of each mirror element.

In FIG. 16, the vertical axis indicates the deflection angle of amirror, defined as “ON” or “OFF” based on the incident light, and theoutput of a light source. The output of the light source is defined as“ON” when the light source outputs the incident light that projects animage and “OFF” when the power supply of the light source is completelyshut off. Furthermore, the horizontal axes indicate the elapsed time. Itis assumed that there are n-pieces of individual mirror elements, whichare represented by Pixels 1 through n. Moreover, the Pixel 3 is assumedto be a mirror element with maximum brightness (i.e., the brightestpixel), producing the maximum intensity of reflection light (i.e., theintensity of the ON light state) to the projection light path.

Referring to FIG. 16, the brightest pixel 3 is in an ON state until timed₄. All the other mirror elements end the ON state by time d₄. Untiltime d₄, the brightest pixel 3 remains in an ON state, the ON state ofthe pixel 2 ends at time d₁, the ON state of the pixel 1 ends at timed₂, and the ON state of the pixel n ends at time d₃. At time d₄, theoutput of the light source and the deflection angle of the mirror orpixel 3 are synchronously turned OFF. This series of operation concludesone frame. Such a control can also be carried out for a sub-frame.

As described above, the light source is synchronized with a mirrorelement of maximum brightness, and when the mirror element with themaximum brightness reflects incident light to the ON state, the othermirror elements stop reflecting their incident light to the ON state.Outside such a time, the light source is turned off. As a result, duringthe transition operation of mirror elements, unstable reflection of theincident light can be eliminated, producing a clear image. This is notthe case for a mirror element with the maximum brightness within oneframe or sub-frame period.

Particularly, it is preferable to turn on the light source when eachmirror stops and is ready to continue the ON state, and to turn off thelight source immediately before a mirror element that is the last to beprojected enters an OFF state for reflecting incident light.

Furthermore, the present control scheme causes each mirror element tooperate in an ON position for one frame or sub-frame by way of a pulsewidth modulation (PWM) control, and to reflect the incident light to theOFF position, in the midst of the ON position of each mirror element.

During the period the mirror element with the maximum brightness (notedas “the brightest mirror element”) reflects the incident light to the ONposition, the other mirror elements finish reflecting the incident lightto the ON position, and furthermore, each mirror element deflects to theOFF state to reflect the incident light during the ON state of eachmirror element. Here, it is assumed that each mirror element is under aPWM control using non-binary data.

FIG. 17 is a timing diagram that shows each mirror element within oneframe carrying out an OFF state while synchronizing a light source,according to the present embodiment. In FIG. 17, the vertical axisindicates the deflection angle of a mirror and the output of a lightsource, with the deflection angle defined as “ON” when the incidentlight comprises an ON light, and that of the mirror defined as “OFF”when the incident light comprises an OFF light. The output of the lightsource is defined as “ON” when the light source outputs the incidentlight that projects an image, and “OFF” when the power supply to thelight source is completely shut off. Furthermore, the respectivehorizontal axes indicate the elapsed time. It is assumed that there aren-pieces of individual mirror elements, each represented by Pixels 1through n. The figure delineates the control for each mirror elementwithin one frame. Other assumptions are that the output of the lightsource is turned ON between the time e₁ and e₉; and Pixel 3 is themirror element that produces the maximum intensity of reflection light(i.e., the intensity of ON light state) toward a projection light path.

At time e₅: the brightest Pixel 3 is in an OFF state. The other pixelscannot turn ON while the brightest Pixel 3 is in an OFF state at thetime e₅. While the mirror element with the maximum brightness is in anOFF state, the other mirror elements cannot be in an ON state. So allmirror elements are in the OFF state, resulting in a black image.

Between the time e₁ and time e₅ which is the period when the brightestPixel 3 is in the ON position, Pixel 2 is in an OFF position at the timee₂, Pixel 1 is in the OFF state at the time e₃, and the Pixel n is inthe OFF state at time e₄. Then, at time e₅, the brightest Pixel 3 is inthe ON state immediately after being in the OFF state. Then, after thebrightest Pixel 3 is in the ON position, the other elements respectivelyfollow.

Therefore, Pixel n is in the ON state at time e_(6:), Pixel 1 at timee₇, and Pixel 2 at time e_(8:). Then, at time e₉: the output of thelight source is turned OFF, finishing one frame. Note that this controlscheme can also be carried out for sub-frames. Meanwhile, in FIG. 17,the output of the light source is turned ON in the midst of the OFFstate of the mirror element with the maximum brightness. However, it isalso possible to turn ON/OFF the output of the light sourcesynchronously with the OFF or ON state of the mirror element with themaximum brightness. Further, it may also be possible to synchronize thestart and finish of the ON and OFF states of other mirror elements withthat of the mirror element with the maximum brightness.

As described above, all mirror elements move to the OFF position fromthe ON position of the individual mirror elements within the period ofone frame or sub-frame. As a result, the light and shade are enhanced byinserting a black image between individual frames or sub-frames toimprove image quality. Meanwhile, turning off the light source makes itpossible to reduce the power consumption and heating of the spatiallight modulator. The mirror device comprising such controlled mirrorelements can also be used for a projection apparatus. For example, asingle-panel projection apparatus, which is described above in FIGS. 3and 4 comprise one or a plurality of mirror devices, respectively.

Embodiment 3

According to the present embodiment, a mirror device is configured toarrange a plurality of mirror elements as array of mirror elements eachcomprising both a deflectable mirror, supported by an elastic hingeformed on a substrate which reflects the incident light emitted from alight source. A single address electrode is asymmetrical formed betweenthe left and right sides, about the deflection axis of the mirror placedon the substrate. Furthermore, the light source is turned off during theperiod in which the mirror performs a series of operations starting fromthe mirror's initial state to the completion of the mirror deflection ofone side of the single address electrode after deflecting to the otherside. The light source may be implemented as a single semiconductorlight source such as a laser light source.

The following three spatial light modulators 5100 is a description ofone mirror element that comprises a mirror device according to thepresent embodiment.

FIGS. 18A, 18B, 18C and 18D are cross-sectional diagrams of the mirrorelement 8600 according to the present embodiment, and respectively showthe initial state, ON state, OFF state and oscillation state of mirror8602. FIG. 18E is a conceptual diagram showing the configuration of onemirror element 8600 according to the present embodiment.

The mirror element 8600 according to the present embodiment illustratedin FIGS. 18A through 18D include one drive circuit as shown in FIG. 18E.The mirror element 8600 according to the present embodiment shown inFIG. 18A includes, on the substrate 8607, one drive circuit used fordeflecting the mirror 8602 shown in FIG. 18E. Furthermore, an insulationlayer 8608 is on the substrate 8607, and one elastic hinge 8604 isformed on the insulation layer 8608. One elastic hinge 8604 supports onemirror 8602, and a singular address electrode 8603, connected to onedrive circuit, is formed under one mirror 8602. One mirror 8602 in thisconfiguration is electrically controlled by a single address electrodeand connected to one drive circuit. Moreover, a hinge electrode 8606connected to the elastic hinge 8604 is grounded by penetrating theinsulation layer 8608.

The drive circuit shown in FIG. 18E requires only one electrode to applya voltage, making it possible to eliminate the two memory cells thatcorrespond to two address electrodes 5116 and 5116 (refer to FIG. 11),leaving only the memory cell 4014. This configuration enables areduction in the number of wirings required to control the deflection ofthe mirror 8602. Incidentally, other exemplary embodiments are the sameas those described for FIG. 11, therefore their descriptions are notprovided here.

One mirror element 8600 is configured according to the presentembodiment as described above. Furthermore, the mirror device iscomprised by placing a plurality of the above described mirror elements8600 on the substrate 8607.

The single address electrode 8603 of mirror element 8600 as describe isexposed above the substrate 8607 shown as the “first electrode part” forthe right one and as the “second electrode part” for the left one, withthe deflection axis of the elastic hinge 8604 or mirror 8602 acting asthe border. The design is such that a Coulomb force is generated eitherbetween the mirror 8602 and the first electrode part or between themirror 8602 and second electrode part by applying a voltage to thesingle address electrode 8603. The phrase “applying a voltage,” noted inthe present specification document can be rephrased to “changing anelectric potential according to a predetermined waveform”.

Note that the Coulomb force F generated between the mirror 8602 and thefirst electrode part or between the mirror 8602 and second electrodepart is represented by the following expression (1):

$\begin{matrix}{{F = {{\frac{1}{4\;\pi\; r^{2}} \cdot \frac{1}{ɛ}}q_{1}q_{2}}};} & (1)\end{matrix}$where “r” is the distance between the mirror 8602 and the firstelectrode part or the distance between the mirror 8602 and secondelectrode part, “∈” is permittivity, “q1” and “q2” are the amount ofcharge retained by the first electrode part (or the second electrodepart) and the mirror 8602.

Determining the Coulomb force F between the left and right sides of themirror 8602 with different forces deflect the mirror 8602 to the left orright of the deflection axis. It is preferable for the angle formedbetween the vertical axis of the substrate 8607 and the deflection angleof mirror, to be symmetrical (between the left and right sides), whenthe mirror 8602 is deflected to the left or right side of the deflectionaxis.

The mirror 8602 is formed with a surface of either a high reflectancemetallic material or a dielectric multi-layer film. Furthermore, theentire hinge or a part (e.g., the base part, neck part or middle part)of the elastic hinge 8604 supporting the mirror 8602 is comprised of ametallic material, possessing a restoration force.

Note that the present specification document depicts the elastic hinge8604 as a cantilever possessing elasticity in a degree that allows afree oscillation of the mirror 8602. The elastic hinge 8604 can also beformed as a torsion hinge. The single address electrode 8603 is made ofa conductive material such as aluminum (Al), copper (Cu), or tungsten(W), and is configured to have the same potential throughout the wholeelectrode. Furthermore, the insulation layer can use, for example, SiO₂or SiC, while substrate 8607 can use Si.

Note that the material and form of each constituent component of themirror device 8600 put forth in the present specification document maybe appropriately changed according to its purpose. In the followingFIGS. 18B through 18D, the single address electrode 8603 and the likeare described as asymmetrical about the elastic hinge or the deflectionaxis of the mirror. Another assumption is that the first electrode partof the single address electrode 8603 is the OFF light side and thesecond electrode part is the ON light side.

As indicated by the cross-sectional diagram of one mirror element shownin FIG. 18A, the initial state of the mirror device according to thepresent embodiment is that the mirror is horizontal to the substrate.For example, in the following description for FIG. 18A, the initialstate of the mirror reflects the incident light 8601 along a directionthat is applied in an image projection system as an intermediate light.FIG. 18B shows a cross-sectional diagram of a mirror element 8600operates in an ON light state of the mirror device, according to thepresent embodiment. Referring to FIG. 18B, a voltage is applied to thesingle address electrode 8603 in the initial state shown in FIG. 18A togenerate a Coulomb force F between the first electrode part (and thesecond electrode part) and a mirror 8602. By forming the secondelectrode part with a larger area than that of the first electrode part,the Coulomb force generated between the second electrode part and theopposite mirror 8602 is larger than the Coulomb force generated betweenthe first electrode part and opposite mirror 8602. The mirror isaccordingly tilted to the second electrode part. The application of avoltage to the single address electrode 8603 deflects the mirror 8602,thereby making it possible to project the incident light 8601 as an ONlight.

FIG. 18C shows a cross-sectional diagram of a mirror element 8600operates in an OFF light state of the mirror device, according to thepresent embodiment. As shown in FIG. 18B, the voltage applied to thesingle address electrode 8603 to control the mirror to operate in an ONstate is turned off. The elastic force of the mirror hinge 8604 causesthe mirror 8602 to oscillate along an opposite direction. With this freeoscillation, the mirror 8602 alternates between the deflection angleproducing the ON light and that producing the OFF light. When thedistance r between the free-oscillating mirror 8602 and a part of thesingle address electrode 8603 producing the OFF light is short, avoltage is re-applied to the single address electrode 8603 at theappropriate time. This regenerates a Coulomb force F between the firstelectrode part and the opposite mirror, and between the second electrodepart and the opposite mirror, respectively. Now, if the distance betweenthe first electrode part and mirror is short and that between the secondelectrode part and mirror is long, the coulomb force of the firstelectrode part is larger than that of the second electrode part becausecoulomb force decreases proportionately to the second power of thedistance. Therefore, the mirror attracted to the first electrode partcontacts the single address electrode 8603, thereby the mirror 8602produces the OFF light.

Then, when the mirror 8602 is horizontal to the substrate, as in theinitial state, an appropriate pulse voltage is applied to the singleaddress electrode 8603 at the position of the free-oscillating mirror8602, causing it to stand still. To return to the initial state in theconventional technique, appropriate voltages are applied to two singleaddress electrodes 8603, generating similar coulomb forces that cause amirror to stand still. In contrast, the present invention applies apulse voltage to the single address electrode 8603, making it possibleto return the mirror 8602 to the initial state. As described above, itis possible to control the ON and OFF light of the incident light byinputting a voltage to the single address electrode 8603. Therefore,each mirror can be independently controlled by a smaller number of theaddress electrodes than in the conventional method. Furthermore, aconfiguration with only one address electrode makes it possible toreduce the number of drive circuits connected to the address electrodeto one. Unlike with the conventional technique, this configuration makesit possible to further reduce the size of the mirror device.

As shown in FIG. 18D the free oscillation of a mirror between thedeflection angle of the mirror producing the ON light and that of themirror producing the OFF light, and the definition of the intensity ofan intermediate light, controls the intensity of reflection toprojection path. FIG. 18D shows that the free oscillation of mirror 8602causes the continuous repetition of the ON light state, intermediatelight state and OFF light state. Furthermore, controlling the number ofrepetitions and the like controls the intensity of the incident lightreflected to a projection light path. Therefore, accumulation of theincident amount of light (“light volume” hereinafter), which are eachreflected toward the projection light path per cycle, makes it possibleto control an amount of the intermediate light between the complete ONstate and that in the complete OFF state. The single address electrodecontrols the intensity of light reflected by one mirror under at leastthree states, i.e., the ON light, intermediate light and OFF light.Therefore, the intensity of light reflecting the projection light pathcan be adjusted appropriately. Furthermore, it is also possible tochange the respective heights of the first electrode part and secondelectrode part of the single address electrode shown in FIGS. 18Athrough 18D. It is also possible to add a stopper or implement othersimilar configurations.

In FIGS. 18A through 18D, the initial state of the mirror, the state ofthe mirror that is retained on the first electrode part and the stateretained on the second electrode part may be assigned to an ON lightstate, OFF light state and intermediate state. Adjustment to therestoring force of the elastic hinge according to different operationalrequirements can also adjust the operation of the free oscillation.Incidentally, the single address electrode may have asymmetrical elasticproperties relative to the deflection axis of the mirror.

FIG. 19 is a cross-sectional diagram showing an exemplary modificationof the mirror element 8600 according to the present embodiment. Themirror element 8600 in FIG. 19 uses materials with differentpermittivity values on the upper parts between the first and secondelectrode parts of the single address electrode 8603. Such aconfiguration makes it possible to control the mirror 8602 under the ONor OFF light states even if the single address electrode 8603 is formedsymmetrically. As FIG. 19 shows, the mirror element 8600 is formedsymmetrically about the elastic hinge 8604 when materials with differentpermittivity values are used. Note that the form of the single addresselectrode 8603 may be modified appropriately. In the case of a mirrorproduced by base materials Si or SiO₂, it is preferable to have high-kmaterials with different and high permittivity values, which includeSi₃N₄ and HfO₂, and are compatible with the process of reducing the sizeof a single semiconductor. In another method, materials with differentpermittivity values can be used for the first and second electrode partsof the upper part of the single address electrode 8603 to control mirror8602 under the ON and OFF light state.

The following is a brief description of a control method for a mirrorelement shown in FIG. 19. When mirror 8602 is deflected from the initialstate, applying a voltage to the single address electrode 8603 makes itpossible to tilt the mirror 8602 to one side with low permittivity basedon the expression (1). The reason is that one side of the single addresselectrode 8603 has a smaller permittivity ∈ in terms of the expression(1 than the other side, which has a larger permittivity value, andtherefore a stronger coulomb force to the mirror 8602 in the initialstate. The mirror 8602, tilted from the initial state, is changed to afree oscillation state by temporarily changing the voltage of the singleaddress electrode 8603 to “0” volts. An appropriate voltage is appliedto the single address electrode 8603 when the freely oscillating mirror8602 gets close to it on the ON or OFF light side. As a result, the ONor OFF light state controls mirror 8602 when it is in the first orsecond electrode side. This is because the distance r between the mirror8602 and single address electrode 8603 has a larger influence on theCoulomb force F than the permittivity ∈ does. Therefore, applying avoltage to the single address electrode 8603 when the distance r has alarger influence makes it possible to tilt the mirror 8602 to the ON orOFF light side.

The above-described operation the mirror 8602 is controlled to operatefrom the initial state to the OFF or ON light state. Furthermore, themethod for controlling the mirror 8602 from the ON or OFF light state tothe initial state is similar to that of the mirror element shown inFIGS. 18A through 18D. It is possible to return the mirror 8602 to theinitial state from the ON or OFF light state by applying an appropriatepulse voltage. For example, the mirror 8602 performs a free oscillationby reducing the voltage applied to a corresponding single addresselectrode 8603 to “0”. Then, when there is an appropriate distance rbetween the single address electrode 8603 and mirror 8602, a voltage istemporarily applied to the single address electrode 8603, while themirror 8602, which performs a free oscillation, moves to a new side. Asa result, a coulomb force F pulls the free-oscillating mirror 8602 to adifferent side from the side it had been headed towards. Acceleratingtoward a different direction makes it possible to return the mirror 8602from to the initial state. Therefore, applying a pulse voltage to thesingle address electrode 8603 shifts the mirror from the ON or OFF lightstate to the initial state.

It is preferable that the non-binary data obtained by converting binarydata controls mirror 8602, as shown in the conversion methods describedin FIGS. 12, 13, 14 and 15. Note that the PWM uses non-binary data tocontrol mirror 8602 in the present embodiment.

As described above, in the case of the single address electrode 8603that controls the mirror 8602, a “dummy operation” is required to tiltthe mirror 8602 from the initial state to a side in which the coulombforce between the mirror 8602 and single address electrode 8603 issmaller or larger The present embodiment is configured to turn off thelight source synchronously with the mirror device carrying out the dummyoperation.

The following is a description of the operation for turning off thelight source synchronously with the mirror device carrying out a dummyoperation.

FIG. 20 is a timing diagram for illustrating the time sequence forturning off a light source synchronously with a dummy operation of eachmirror element. In FIG. 20, the vertical axis shows the deflection angleof the mirror, which is defined as “ON” or “OFF” based on theconstitution of the incident light, the voltage applied to an electrodeand the output of a light source. Furthermore, a voltage is defined as“Von” when it is applied to a single address electrode and as “0 V” whenit is not. Moreover, the output of a light source is defined as “ON”when outputting the image projected by the incident light, while it isdefined as “OFF” when the power for the light source is completely shutoff. The respective horizontal axes represent elapsed time. The graphsshow that in the initial state, the deflection angle of a mirror on aside where the Coulomb force between the mirror and single addresselectrode is large is “ON”, while the deflection angle of the mirror onthe side where the Coulomb force between the mirror and single addresselectrode is small is “OFF”.

The light source is completely shut off until time f₁: to maintain thevoltage at “0”, thereby keeping the deflection angle of mirror at itsinitial state.

The light source is OFF at time f₁:, and a voltage is applied to thesingle address electrode to make it Von. As a result, the mirror isdeflected to the ON deflecting angle, where the Coulomb force betweenthe mirror and single address electrode is large.

While the light source is OFF, the voltage is applied to the singleaddress electrode until time f₂. Accordingly, the mirror is maintainedat the ON deflection angle to abut the single address electrode.

While the light source is OFF, the application of the voltage to thesingle address electrode is stopped at “0” volts at time f₂:, resultingin a free oscillating mirror.

While the light source is OFF, the voltage to the single addresselectrode is at “0” volts until time f₃. As a result, the mirrorcontinues to freely oscillate and shifts from the ON to the OFFdeflection angle.

At time f₃: when the mirror approaches the OFF deflection angle, avoltage Von is applied to the single address electrode. As a result, themirror abuts on the single address electrode to maintain the OFFdeflection angle. As described above, the operation between the timef_(1:), the initial state of the mirror, and the time f_(3:), when themirror is retained on the side with a smaller Coulomb force (in theinitial state), is referred to as a “dummy operation”. Then, followingthe completion of the dummy operation the deflection angle of the mirroris deflected to an OFF direction, the output of the light source issynchronously turned ON.

As described above, through the operation of causing the light source tosynchronously turn off with the mirror device when it is performing adummy operation, makes it possible to eliminate an unstable reflectionof light, while the mirror is moving under a deflecting operation. Aprojection apparatus comprising such a mirror device is capable ofeliminating an unstable reflection of light while the mirror isdeflecting, thereby improving the image quality. Projection apparatusescomprising mirror devices are single and multi-panel, as described abovein FIGS. 3 and 4, respectively.

Embodiment 4

The present embodiment is configured to array a plurality of mirrorelements, which each comprises both an address electrode placed on asubstrate under the mirror and a deflectable mirror, which is supportedby an elastic hinge set on a substrate and which reflects the incidentlight emitted from a light source. Furthermore, the present embodimentis configured to retain the mirror, during a period of time the lightsource is turned off, in a deflecting direction that is the reverse ofthe direction in which the mirror is reflected at the end of a periodwhen the light source is turned on. It is preferable that the time toreversely deflect the mirror is proportional to the time it takes todeflect the mirror at the end of the light source's turn-on period.

The mirror elements according to the present embodiment are, forexample, configured as shown in FIGS. 10, 11, 18A, 18B, 18C, 18E and 19.The light source may be implemented as a single semiconductor lightsource such as a laser light source. Furthermore, it is preferable tocontrol a mirror with non-binary data obtained by converting binarydata, as described in FIGS. 12, 13, 14 and 15.

The following describes the reverse deflection of the mirror when thelight source is turned off. When the light source is turned off, thetime it takes to retain the mirror in reverse is proportional to thetime it takes to deflect the mirror at the end of the turn-on period ofthe light source. It is assumed that each mirror is controlled by PWMusing non-binary data.

FIG. 21 is a timing diagram for illustrating the synchronization of thelight source and the deflection angle of each mirror element. Thevertical axis in FIG. 21 indicates the deflection angle of a mirror andthe output of a light source, with the deflection angle of the mirrordefined as “ON” or OFF based on the constitution of the incident light.Furthermore, the output of the light source is defined as “ON” when itcan output an incident light to project an image, and “OFF” when thepower supply of the light source is completely shut off. Moreover, therespective horizontal axes represent the elapsed time. The assumption isthat there are n-pieces of individual mirror elements, with theindividual mirror elements represented by Pixels 1 through n. The figuredelineates the control of each mirror element within one frame.Furthermore, Pixel 3 is assumed to be a mirror element with maximumbrightness (i.e., the brightest pixel), which is the mirror element thatproduces the maximum intensity of reflection light to a projection lightpath and that remains ON for the longest period of time. Furthermore,the period in which Pixel 3 produces the maximum brightness is ON and issynchronized with the period in which the light source is ON. Then, atthe time g₄ the brightest Pixel 3 and the light source are both turnedfrom ON to OFF. All mirrors are ON, and the light source and Pixel 3 aresynchronously ON until time g₁:.

Between time g_(1:) and time g_(4:), the time length the brightestPeriod 3 is ON, the Pixel 2 turns OFF at time g_(1:), the Pixel n turnsOFF time g₂, and Pixel 1 turns OFF at time g_(3:), while the lightremains ON. At time g₄: the brightest Pixel 3 turns OFF andsynchronously with Pixel 3, the light source is turned OFF. Then, eachmirror is retained at the opposite direction from the direction it wasdeflected when the light source was turned off for a time period that isproportional to the time period the mirror was deflected Here, thelength of time the mirror takes to deflect when the light source is off,is the longest for the Pixel 3, then Pixels 2, n and 1. Therefore Pixel3 continues to be deflected to OFF between the time g_(4:) and g_(9:).Then, Pixel 2 turns ON and keeps the mirror deflection angle ON betweenthe time g_(4:) and time g_(8:). Then, the Pixel n, turns ON and keepsthe mirror deflection ON between the time g_(6:) and g_(8:). Then, thePixel 1, turns ON and keeps the mirror deflection angle along an ONdirection between the time g_(5:) and g_(7:).

As described above, a mirror is retained at the opposite direction fromthe direction it was deflected when the light source is turned off.Furthermore, length of time it takes to keep the mirror in the reversedirection when the light source is turned off is proportional to thelength of time it takes the mirror to deflect it at the end of theturn-on period of the light source. Note that retaining the mirror inthe inverse direction during the turn-off period of the light source isbased on data that is different from the non-binary data that controlsthe mirror during the turn-on. In the following description, the “firstcontrol data” controls the mirror during a turn-on period of the lightsource, while the “second control data” controls the mirror during theturn-off period. Incidentally, the first control data corresponds to thedata input to the bit line 5121-1 and bit line 5121-2, which areillustrated in FIGS. 11 and 18E.

The second control data has an inverse polarity opposite to that of thefirst control data immediately before the light source is turned off.Therefore, the second control data is obtained, for example in thefollowing procedure. First, the first control data received immediatelybefore the light source is turned off is stored. In this event, it ispreferable to also store the time of each mirror's last deflectionreferred to as the “final deflection time”). Then, the operation standsby until the light source is turned off.

To obtain the second control data, the polarity of the first control isinverted when the turn-off of the light source is complete. With thesecond control data, the mirror is deflected to a direction that isdifferent from the deflecting direction of the first control data at theend of the turn-on period of the light source. Note that it ispreferable that the control for inverting the polarity of the bit lineis carried out in the units of word line. Meanwhile, the second controldata may be temporarily retracted from the bit line by storing it inframe memory or by the like operation. This operation makes it possibleto control the time to retain a mirror in the reverse deflectingdirection in accordance with the final deflection time storedimmediately before the turn-off of the light source.

The control operations as that shown in FIG. 21 can also be carried outfor a sub-field. Note that, in the present embodiment, a sub-frame isdefined as data assigned to each different colors of light projected atdifferent wavelengths when a projection apparatus projects a pluralityof incident lights with different wavelengths in sequence.

Therefore, tilting a mirror opposite the direction of deflection duringthe period the light source is turned off prevents the elastic hinge ofthe mirror from deforming. As a result, the life of the mirror device isextended. Furthermore, such a mirror device can also be used for aprojection apparatus. As described in FIGS. 3 and 4, respectively,single and multi-panel projection apparatuses comprise mirror devices.

Embodiment 5

A mirror device according to the present embodiment is configured toarray a plurality of mirror elements each comprising both an addresselectrode placed on a substrate under the mirror and a deflectablemirror, which is supported by an elastic hinge set on a substrate andwhich reflects the incident light emitted from a light source.Furthermore, the present embodiment is configured so as to not applyvoltage to the address electrode during the period in which the lightsource is turned off. The mirror elements according to the presentembodiment are, for example, configured as illustrated in FIGS. 10, 11,18A, 18B, 18C, 18E and 19. The light source may be implemented as asingle semiconductor light source such as a laser light source.

Furthermore, it is preferable to control a mirror by using non-binarydata obtained from the conversion of the binary data as shown in FIGS.12, 13, 14 and 15.

The following is a description of the control process by not applyingvoltage to the address electrode during the period in which the lightsource is turned off. The assumption is that PWM controls each mirrorelement using the non-binary data.

FIG. 22 is a timing diagram for illustrating the synchronization of alight source, an address electrode and the deflection angle of eachmirror element. In FIG. 22, the vertical axis is the deflection angle ofa mirror, which is “ON” or “OFF” based on the constitution of theincident light, the voltage applied to an electrode and the output of alight source. Furthermore, a voltage applied to an electrode is definedas “Von” when a voltage is applied to a single address electrode and as“0 V” when a voltage is not applied. Moreover, the output of a lightsource is “ON” when outputting the incident light that projects animage, while the output is “OFF” when the power for the light source iscompletely shut off. Furthermore, the respective horizontal axesrepresent the elapsed time.

Until the time h₁:, the deflecting angle of mirror is controlled tooperate between the ON and OFF states, which is the deflecting angle ofthe initial state, and no voltage is applied to the address electrode,i.e., “0” volts. The assumption here is that the light source is ON. Attime h₁: a voltage Von is applied to the address electrode to controlthe mirror to deflect to an ON direction from the initial state and thelight source is turned ON. Between time h₁ and h₂: the voltage is keptapplied to the address electrode, making it Von, to position thedeflection angle of mirror OFF, and the light source is turned ON. Attime h₂: the voltage applied to the address electrode is turned OFF torelease the deflecting angle of the mirror from the OFF state. As aresult, the mirror starts performing a free oscillation, and, the lightsource is turned off. The turn-off of the voltage applied to the addresselectrode causes the electric charge to discharge from the ON capacitor5115 b and/or OFF capacitor 5116 b, as shown in FIGS. 11 and 18E. Thedischarge of electricity from a capacitor is accomplished by inputting,for example, “0” volt data to the bit lines 5121-1 and 5121-2 andselecting the word line 5131 in the configuration illustrated in FIG.11.

Note that the voltage applied to the address electrode is now cut off,and the state after electricity is discharged from the capacitor is thesame as the initial state. After time h₂: while the light source is OFF,the mirror is left to perform the free oscillation without applying avoltage to the address electrode. This is accomplished by not selectingthe word line 5131 while the light source is turned OFF as illustratedin FIG. 11. It is alternatively accomplished by inputting data, such asapplying “0” volts to the bit lines 5121-1 and/or 5121-2, with whichelectricity is not charged to a capacitor when the light source isturned OFF as in the mirror element shown in FIG. 18E.

As described above, an operation by not applying voltage to the addresselectrode of the mirror device when the light source is turned offreduces the consumption of power necessary to drive the mirror deviceand alleviates the heat generated. Note that a voltage may besynchronously applied to the address electrode of the mirror device withthe transition from turn-off to a turn-on state of the light source,though it is not shown in FIG. 22. Furthermore, such a mirror device canalso be used for a projection apparatus.

Application of the control processes may be implemented in imageprojection systems that include single and multi-panel projectionapparatus, described in FIGS. 3 and 4, respectively, which comprisemirror devices. It is desirable for the illumination light and/or theprojection light of a projection apparatus according to the presentembodiment to be a polarized light, which comprises a polarizationcontrol unit.

The control processes may be implemented in exemplary embodimentsincluding a liquid crystal device such as LCD and LCOS controls thepolarizing direction. The projection apparatus may comprise a controlcircuit that controls the emission light intensity and timing of thelight source, and a polarization control unit, placed in theillumination light path from the light source or a projection light paththat controls the transmission light intensity. The polarization controlunit is a commercial product called a color switch that is produced bycombining a liquid crystal with a polarization filter. Furthermore, thepolarizing direction of the light of a plurality of wavelengths canpossibly be controlled by polarization control unit.

Furthermore, it is preferable for a projection apparatus with aconfiguration that a mirror device is used as a spatial light modulatorfor a specific color of light has and has a different polarizingdirection from that of a light of different colors projected at adifferent wavelength.

Furthermore, it is preferable that a projection apparatus is configuredsuch that a mirror device is used as a spatial light modulator, and suchthat the same mirror device modulates illumination lights of differentcolors and the lights have different polarizing directions andtransmitted with different wavelengths, respectively.

For example, when at least one mirror device modulates both illuminationlights in two colors with different polarizing directions in a two-panelprojection apparatus, placing a transmissive optical element, such as anLCD, in the projection light path, makes it possible to project only thelight of a specific polarizing direction. Furthermore, the lights ofrespective colors can be projected in sequence by changing over thestates of the LCD in accordance with the color of an image signal inorder to separate polarized lights.

Furthermore, when an optical element, such as a polarizing beam splitter(PBS) for separating a polarized light, is placed in the projectionlight path, the wavelengths of light transmitting through the PBS can bechanged over in sequence by changing the polarizing directions of theillumination lights of two colors with a color switch.

Sequentially changing over polarizing directions also enables, theadjustment of light intensity by comprising sub-light sources.Configuring a light source appropriately sets the number of emittingsub-light sources, positions each wavelength of the light and changesover the sub-light sources in sequence based on the desired polarizingdirection.

In this event, the voltage applied to the address electrode is cut offin the mirror device deflecting the illumination light emitted from thesub-light source that is turned off due to the changeover. When themirror device deflects the illumination lights emitted from a pluralityof sub-light sources, however, the voltage applied to the addresselectrode will be cut off only when the sub-light sources are turnedoff.

Note that the light source may include sub-light sources emitting thelights of the same wavelength, and the lights have different polarizingdirections. Furthermore, the sub-light sources may be made to emit lightso that the lights of the same wavelength possess any one or a pluralityof polarizing directions.

Furthermore, polarizing directions can be changed 90 degrees bytransmitting a linear-polarized light through two pieces of λ/4 plates.It is desirable for the two pieces of λ/4 plates to be placed with thepolarization axes 90 degrees apart. The polarizing directions of lightcan be sequentially changed by either transmitting or not transmittingthe light through the two λ/4 plates. Furthermore, there may be one λ/4plate with light transmitting through it reflected by a surface that isplaced at a later stage.

It is further preferable that the light transmitting through the λ/4plate is reflected by a reflection surface placed at a later stage ofthe aforementioned λ/4 plate in the light path and then the light istransmitted through the same λ/4 plate. The spatial light modulator is amirror device, and it is possible for a projection apparatus toimplement two mirror devices that modulate the illumination lightshaving different polarizing directions about the same wavelength.

The projection apparatus is configured such that one mirror devicemodulates the lights are transmitted as color lights with red and greenwavelengths while the other mirror device modulates the lightspossessing green and another color light transmitted with bluewavelengths. In this case, the configuration is such that the linearpolarization lights with which the directions of the respective greenlights differ by 90 degrees are irradiated on the respective mirrordevices. Then, the control circuit for the mirror device that changesthe intensities and emission periods of the four lights modulates theindividual lights, making it possible to adjust the different grayscales and brightness of the individual lights. Then, the modulatedindividual lights are synthesized, and can be projected by way of aprojection optical system.

Furthermore, the spatial light modulator preferably modulates theindividual lights on the basis of image signals that correspond to thelights of different wavelengths. The colors of the illumination lightswith different wavelengths can be, for example, cyan, magenta, yellowand white.

It is preferable for a projection apparatus to be configured to use asingle semiconductor light source; the spatial light modulator, isimplemented with a mirror array including one to two million pixels thateach control the reflection of the illumination light emitted from thelaser light source, with a deflectable mirror that deflects thereflecting direction of modulated illumination light either ON or OFFtowards a projection path. The deflection angle of the mirror of themirror element in an exemplary embodiment is between ±9 degrees and ±4degrees clockwise (CW) from the initial state. The F-number of theprojection lens of the projection optical system is between 3 and 7.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alternationsand modifications will no doubt become apparent to those skilled in theart after reading the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alternations andmodifications as fall within the true spirit and scope of the invention.

1. A projection apparatus, comprising: a mirror device includes a firstelectrode and a second electrode with an elastic hinge disposed betweenthe first electrode and second electrode for supporting a mirrorcontrolled by applying a voltage to the first and second electrodes todraw the mirror with a Coulomb force toward one of said electrodes; alight source for emitting a light for projecting to the mirror formodulating and then reflected by the mirror, wherein the light source iscontrolled to coordinate with a designated operation of the mirror tosuppress an emission of the light during a period when the mirrorperforms the designated operation; and the first electrode and thesecond electrode are connected to a single drive electrode for applyingthe voltage to the first and second electrodes and wherein the firstelectrode and the second electrode having different permittivities. 2.The projection apparatus according to claim 1, wherein: the light sourceis controlled to suppress an emission of the light during a period whenthe mirror performs the designated operation of changing from a firstdeflection state of operation with the mirror deflect to a first angleto a second deflection state of operation the mirror deflected to asecond angle.
 3. The projection apparatus according to claim 2, furthercomprising: a controller to control the mirror to operate in at leastthree states including a non-deflection state when said mirror is in anatural non-deflection position, a first deflection state and a seconddeflection when said mirror is deflected to a first deflection angle anda second deflection angle respectively.
 4. The projection apparatusaccording to claim 3, wherein: the first electrode and the secondelectrode have different cross section areas facing the mirror forgenerating different drawing forces to deflect the mirror toward thefirst and second electrodes.
 5. The projection apparatus according toclaim 1, wherein: the mirror device further comprises a main powersupply for supplying power to said light source, and the designatedoperation of the mirror is carried out after the main power supply isturned on.
 6. The projection apparatus according to claim 1, wherein:the light source suppresses the emission of the light during a periodwhen the mirror performs the designated operation.
 7. A projectionapparatus comprising: a mirror device includes a first electrode and asecond electrode with an elastic hinge disposed between the firstelectrode and second electrode for supporting a mirror controlled byapplying a voltage to the first and second electrodes to draw the mirrorwith a Coulomb force toward one of said electrodes; a light source foremitting a light for projecting to the mirror for modulating and thenreflected by the mirror, wherein the light source is controlled tocoordinate with a designated operation of the mirror to suppress anemission of the light during a period when the mirror performs thedesignated operation; and, the first electrode and the second electrodehave different permittivities.
 8. A projection apparatus comprising: amirror device includes a first electrode and a second electrode with anelastic hinge disposed between the first electrode and second electrodefor supporting a mirror controlled by applying a voltage to the firstand second electrodes to draw the mirror with a Coulomb force toward oneof said electrodes; a light source for emitting a light for projectingto the mirror for modulating and then reflected by the mirror, whereinthe light source is controlled to coordinate with a designated operationof the mirror to suppress an emission of the light during a period whenthe mirror performs the designated operation; and, the light source iscontrolled to suppress an emission of the light during a period when themirror performs the designated operation of changing from a naturalnon-deflection state to a first deflection state of operation with themirror deflect to a first deflection angle, and also during a periodwhen the mirror changing from said first deflection state to a seconddeflection state of operation with the mirror deflected to a seconddeflection angle.
 9. A projection apparatus comprising: a mirror deviceincludes a first electrode and a second electrode with an elastic hingedisposed between the first electrode and second electrode for supportinga mirror controlled by applying a voltage to the first and secondelectrodes to draw the mirror with a Coulomb force toward one of saidelectrodes; a light source for emitting a light for projecting to themirror for modulating and then reflected by the mirror, wherein thelight source is controlled to coordinate with a designated operation ofthe mirror to suppress an emission of the light during a period when themirror performs the designated operation; and, the mirror device iscontrolled with externally inputted image data, and the designatedoperation is carried out after completing display of each frame of theimage data.
 10. A method for controlling and operating an imageprojection apparatus implemented with a light source projecting a lightto a mirror device having a plurality of micromirrors deflectable todifferent deflection states for modulating and reflecting the light forprojecting images, the method comprising: controlling an intensity ofthe light projected from the light source by suppressing the lightintensity during an entire time period when the micromirrors arecontrolled in a non-deflection state; and continue to suppress the lightintensity during the entire time period when the micromirror isdeflected to move from the non-deflection state to a deflection state;and controlling the light source to project a normal intensity for imagedisplay when said micromirror is stabilized in the deflection state. 11.A method for controlling and operating a projection apparatusimplemented with a light source projecting a light to a mirror devicehaving a plurality of micromirrors each includes electrodes forreceiving voltages to deflect to different deflection states formodulating and reflecting the light for projecting images, the methodcomprising: controlling an intensity of the light projected from thelight source by suppressing the light intensity during an entire timeperiod when the micromirror is controlled in a non-deflection state; andapplying a voltage to the electrodes to control and deflect themicromirror to a first deflection state followed by turning off thevoltage applied to the electrode for deflecting the micromirror to asecond deflection state according to a natural elastic force of a hingesupporting the micromirror; and controlling the light source to projecta normal intensity for image display when said micromirror is stabilizedin the second deflection state.
 12. The method for controlling andoperating a projection apparatus according to claim 11, wherein: saidstep of applying voltages to said electrode further comprising applyinga same voltage to a first electrode and a second electrode forcontrolling the micromirror.